A mobile device such as a smartphone or tablet typically requires an interface such as a Universal Serial Bus (USB) connector to couple to other devices. For example, the USB type-C connector has been widely adopted by the smartphone market. It is now conventional for a USB type-C connector to be the only external interface for such mobile devices. But mobile devices do not just drive other USB devices. For example, mobile devices are being used as video sources to drive displays and televisions with high-definition video such as supported by the DisplayPort protocol. The USB type-C connector must then support not only USB data traffic but also DisplayPort video data traffic.
An example mobile device 100 is shown in FIG. 1 in which a physical layer (PHY) interface 120 supports both the DisplayPort (DP) and the USB 3.0 (USB3) protocols. Since PHY interface 120 supports two protocols, it may also be denoted as a USB3-DP PHY interface 120. A multiplexer (not illustrated) in PHY interface 120 thus selects between incoming DP and USB3 data streams at an input port 125. These data streams are sourced by corresponding controllers. Each controller takes a certain amount of die space yet there is only so much die space adjacent input port 125. It may thus be the case that only one of these controllers can be adjacent to input port 125 on the die for USB3-DP PHY interface 120. In mobile device 100, it is a USB3 controller 130 that is adjacent to input port 125. In contrast, a DP controller 105 is located more remotely on the die from the input port 125.
Due to its remote location, the data stream from DP controller 105 to input port 125 for USB3-DP PHY interface 120 is pipelined using a plurality of sets of flip-flops 110. For example, the data stream from DP controller 105 may comprise a series of digital words (e.g., 60-bit digital words). Due to non-idealities in the transmission line that couples DP controller 105 to USB3-DP PHY interface 120, the individual bits in such relatively-wide digital words would become skewed relative to each other during the propagation from DP controller 105. Flip-flops 110 re-align the bits in the DP data words and thus address this skew. A physical coding sublayer (PCS) module 115 performs PCS processing on the DP data words from flip-flops 110 and presents the processed DP data words to input port 125. A serializer and transmitter (TX) within USB3-DP PHY interface 120 serializes and transmits the DP data words from PCS module 115 to an external receiver (not illustrated). Similarly, the serializer and transmitter within USB3-DP PHY interface 120 serializes and transmits USB data words from USB3 controller 130 as received through input port 125. Although USB3-DP PHY interface 120 eliminates the need for off-chip multiplexing of USB and DP data streams, flip-flops 110 consume considerable die space and power. Moreover, the pipelining through the sets of flip-flops 110 introduces latency.
Accordingly, there is a need in the art for denser and lower-power controller-PHY on-chip interfaces.